The invention relates to liquid crystal compositions suitable for use in electro-optical matrix displays of the twisted nematic cell type, and to an electro-optical matrix display using the liquid crystal composition mentioned above.
There is still a great demand for liquid crystal compositions (LC compositions) suitable for matrix displays having an electrooptical characteristic (contrast/voltage curve) as steep as possible and simultaneously a low threshold voltage. In such matrix displays, each "display point" of an electrode grid can be selectively triggered by applying a voltage to a first electrode layer, consisting of a multiplicity of horizontral rows of conductors, and to another electrode layer, consisting of a multiplicity of vertical rows of conductors (multiplex drive). The highr the multiplex ratio and the lower the maximum voltage of the available drivers, the lower the threshold voltage of the LC composition has to be. A disadvantage of these matrix display elements is the partial activation of display points in the immediate vicinity of a triggered display point, which partial activation is called "crosstalk" and reduces the contrast of the display in an undesirable manner. The steeper the electro-optical characteristic of the LC composition used in a display element of this type, the less such crosstalk is then observed. As a rule, the steepness of the electro-optical characteristic of a LC composition is given as the ratio of the control voltages V which must be applied to a given display element in order to obtain 10% of the maximum contrast (V.sub.10) and 50% of the maximum contrast (V.sub.50).
The steepness of the electro-optical characteristic is the greater, the smaller the ratio ##EQU1## Till today the steepness of the electro-optical characteristic can only be determined by experiment, because all theoretical predictions ended up to now in rather wrong results.
Besides of a decrease of the contrast with increasing multiplex ratio, there is also a strongly increasing viewing-angle dependence of the contrast. This dependence is defined as ##EQU2## wherein V.sub.x,y,z is the applied control voltage at x % contrast, viewing angle y and temperature z.degree. C.
The smaller .beta., the better is the optical performance of the matrix display.